/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:		arm_std_f32.c
*
* Description:	Standard deviation of the elements of a floating-point vector.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupStats
 */

/**
 * @defgroup STD Standard deviation
 *
 * Calculates the standard deviation of the elements in the input vector.
 * The underlying algorithm is used:
 *
 * <pre>
 * 	Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1))
 *
 *	   where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]
 *
 *	                   sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]
 * </pre>
 *
 * There are separate functions for floating point, Q31, and Q15 data types.
 */

/**
 * @addtogroup STD
 * @{
 */


/**
 * @brief Standard deviation of the elements of a floating-point vector.
 * @param[in]       *pSrc points to the input vector
 * @param[in]       blockSize length of the input vector
 * @param[out]      *pResult standard deviation value returned here
 * @return none.
 *
 */


void arm_std_f32(
    float32_t* pSrc,
    uint32_t blockSize,
    float32_t* pResult)
{
	float32_t sum = 0.0f;                          /* Temporary result storage */
	float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
	float32_t in;                                  /* input value */
	uint32_t blkCnt;                               /* loop counter */

#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	float32_t meanOfSquares, mean, squareOfMean;

	/*loop Unrolling */
	blkCnt = blockSize >> 2u;

	/* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
	 ** a second loop below computes the remaining 1 to 3 samples. */
	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
		/* Compute Sum of squares of the input samples
		 * and then store the result in a temporary variable, sum. */
		in = *pSrc++;
		sum += in;
		sumOfSquares += in * in;
		in = *pSrc++;
		sum += in;
		sumOfSquares += in * in;
		in = *pSrc++;
		sum += in;
		sumOfSquares += in * in;
		in = *pSrc++;
		sum += in;
		sumOfSquares += in * in;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
	 ** No loop unrolling is used. */
	blkCnt = blockSize % 0x4u;

	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		/* Compute Sum of squares of the input samples
		 * and then store the result in a temporary variable, sum. */
		in = *pSrc++;
		sum += in;
		sumOfSquares += in * in;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Compute Mean of squares of the input samples
	 * and then store the result in a temporary variable, meanOfSquares. */
	meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);

	/* Compute mean of all input values */
	mean = sum / (float32_t) blockSize;

	/* Compute square of mean */
	squareOfMean = (mean * mean) * (((float32_t) blockSize) /
	                                ((float32_t) blockSize - 1.0f));

	/* Compute standard deviation and then store the result to the destination */
	arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);

#else

	/* Run the below code for Cortex-M0 */

	float32_t squareOfSum;                         /* Square of Sum */
	float32_t var;                                 /* Temporary varaince storage */

	/* Loop over blockSize number of values */
	blkCnt = blockSize;

	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		/* Compute Sum of squares of the input samples
		 * and then store the result in a temporary variable, sumOfSquares. */
		in = *pSrc++;
		sumOfSquares += in * in;

		/* C = (A[0] + A[1] + ... + A[blockSize-1]) */
		/* Compute Sum of the input samples
		 * and then store the result in a temporary variable, sum. */
		sum += in;

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Compute the square of sum */
	squareOfSum = ((sum * sum) / (float32_t) blockSize);

	/* Compute the variance */
	var = ((sumOfSquares - squareOfSum) / (float32_t)(blockSize - 1.0f));

	/* Compute standard deviation and then store the result to the destination */
	arm_sqrt_f32(var, pResult);

#endif /* #ifndef ARM_MATH_CM0 */

}

/**
 * @} end of STD group
 */
